1. Technical Field
The present invention relates to a method for producing carbonyl fluoride.
2. Background Art
Carbonyl fluoride (COF2) is used as a cleaning gas or etching gas for e.g. an apparatus for producing semiconductors, or as a starting material or a fluorinating agent for organic compounds. In such an application, particularly in an application as a cleaning gas for an apparatus for producing semiconductors, highly-pure carbonyl fluoride is desired.
As one of syntheses for carbonyl fluoride, a method of mixing carbon monoxide gas and fluorine gas in a gas phase to react them, is heretofore known (Non-Patent Document 1).
However, the above method had problems such as a danger of explosion, a decrease in the reaction yield of carbonyl fluoride due to a side reaction and vigorous heat generation. Now, such problems will be described in detail.
First, when carbon monoxide and fluorine are used as starting materials, the heat of formation of carbonyl fluoride is remarkably high. Further, the direct fluorination reaction of carbon monoxide using fluorine proceeds at an extremely high speed even at a normal temperature. Accordingly, unless such a heat of reaction is sufficiently removed, the temperature of carbonyl fluoride produced will increase.
Carbonyl fluoride will be decomposed to tetrafluoro methane and carbon dioxide at 300° C. or higher (Non-Patent Documents 2 to 4). Accordingly, unless the heat of reaction is sufficiently removed, it is considered that tetrafluoro methane and carbon dioxide will be produced as by-products.
Carbon dioxide and carbonyl fluoride have close molecular diameters, whereby it is difficult to separate them by adsorption. Further, both of them are readily reacted with an alkaline substance, and therefore, it is also impossible to separate them by neutralization. Furthermore, both of them have close boiling points, and therefore, it is also difficult to separate them by distillation (Patent Document 1). Accordingly, in order to obtain highly-pure carbonyl fluoride, it is extremely important to suppress production of carbon dioxide as a by-product by means of heat removal at the time of the reaction.
On the other hand, for the purpose of solving the above problems, Patent Document 2 proposes a method for producing carbonyl difluoride, characterized in that, when carbonyl difluoride is continuously produced by the reaction of carbon monoxide with fluorine gas, at least one of the third component gases selected from the group consisting of N2, He, Ne and Ar is added, and the reaction is carried out while the gas is flown under dynamic conditions and under reduced pressure.
Patent Document 1: JP-A-2003-212525
Patent Document 2: JP-A-2003-267712
Non-Patent Document 1: Handbook of preparative inorganic chemistry I, 206 2nd ed., Georg Brauer, ed., Academic Press, New York, 1965
Non-Patent Document 2: Ruff; Li, Z. Anorg. Allg. Chem., 242 (1939), 272
Non-Patent Document 3: Li, J. chin, Chem. Soc., 11 (1944), 14
Non-Patent Document 4: Chem. Abstr., (1945), 1099